Can I use java.util.LinkedList to construct a circular/cyclic linked list?

Question

I would like to create a circular/cyclic linked list where the tail of the list would point back to the head of the list. So can I use java.util.LinkedList and modify the tail node after creation of the list to make it circular/cyclic? If so, can you show me some code on how that would happen?

If I can't use java.util.LinkedList, how should I create my own circular/cyclic linked list implementation? Can you show me the skeletons of how this implementation would look?

Let me know if you need more details and I'll clear up any confusion.

I just want to play around with making one. No real reason except for myself. I haven't seen many implementations of this online and I just want to give it a try. — Hristo
@puddingfox: A circular list is useful for round-robin access of a collection (e.g. for load-balancing) — user359996
@user359996: Is using a circular list for round robin just a good programming practise? I understand that 'round' and 'circular' go together, but are there any other reasons for using a circular list over an array list? — Victor
How the circular list is implemented isn't super important. To your point, I personally would use an ArrayList and then wrap it with docs.guava-libraries.googlecode.com/git-history/release/javadoc/…. EDIT: Apparently, that's even one of the answers someone gave... — user359996

Lajos Arpad Lajos Arpad · Accepted Answer · 2010-09-18T18:27:39

class ListNode {
    public ListNode next;
    public Object data;

    public ListNode(Object data, ListNode next) {
        this.next = next;
        this.data = data;
    }
}

class CircularLinkedList {
    private ListNode head = null;
    private int numberOfElements = 0;
    private ListNode actualElement = null;
    private int index = 0;

    public boolean isEmpty() {
        return (numberOfElements == 0);
    }

    public int getNumberOfElements() {
        return numberOfElements;
    }

    public void insertFirst(Object data) {
        if (!(isEmpty())) {
            index++;
        }
        ListNode listNode = new ListNode(data, head);
        head = listNode;
        numberOfElements++;
    }

    public void insertAfterActual(Object data) {
        ListNode listNode = new ListNode(data, actualElement.next);
        actualElement.next = listNode;
        numberOfElements++;
    }

    public boolean deleteFirst() {
        if (isEmpty())
            return false;
        if (index > 0)
            index--;
        head = head.next;
        numberOfElements--;
        return true;
    }

    public boolean deleteActualElement() {
        if (index > 0) {
            numberOfElements--;
            index--;
            ListNode listNode = head;
            while (listNode.next.equals(actualElement) == false)
                listNode = listNode.next;
            listNode.next = actualElement.next;
            actualElement = listNode;
            return true;
        }
        else {
            actualElement = head.next;
            index = 0;
            return deleteFirst();
        }
    }

    public boolean goToNextElement() {
        if (isEmpty())
            return false;
        index = (index + 1) % numberOfElements;
        if (index == 0)
            actualElement = head;
        else
            actualElement = actualElement.next;
        return true;
    }

    public Object getActualElementData() {
        return actualElement.data;
    }

    public void setActualElementData(Object data) {
        actualElement.data = data;
    }
}

Can I use java.util.LinkedList to construct a circular/cyclic linked list?

3 Answers